The present invention relates in general to methods and coatings for increasing the service life of tools, and in particular to a new and useful method of increasing the service life of a machining or forming tool by including an intermediate layer having the formula CrX, between the tool material or substrate and a coating on top of the substrate made of MeX, where X is carbon, oxygen, nitrogen or boron, and Me is at least one group IVb metal. The invention is also directed to a protection-coated tool made according to the method.
The group definition (group IVb) of the periodic system of elements corresponds to the "CRC Handbook of Chemistry and Physics", 46th edition, 1964.
It is known that the layer adhesion of MeX layers of the above defined type, such as for example of titanium nitride layers, is optimal if the substrate surface coated with it is very clean or an Me intermediate layer, in the stated example a titanium intermediate layer, is disposed between the tool substrate and the MeX coating. In this connection reference is made to Stolz et al., Surface Engineering, 1989, Vol. 5, No. 4, 305 or to Jehn et al., Surface and Coatings Technology, Vol. 41, No. 2, 1990, 167.
The reason for this is seen in the optimum anchoring which takes place due to the epitaxial growth of MeX, such as of titanium nitride, on the primary carbides of the tool substrate which is usually steel. In this connection reference is made to Helmersson et al., J. Vac. Sci. Technol. A3, 1985, 308. With respect to further tool coatings, reference is made to patent document GB-A-222633A, EP-A-0470359, GB-A-2110246, FR-A-2110202 and to "Chemical Abstracts", Vol. 93, No. 12, 22 Sept. 1980, Columbus, Ohio, U.S., Abstract No. 118218a: J. Tacijowski et al., "Properties of composite chromium and titanium carbide layers", page 211, column 2; Zusammenfassimg Metalozn Obrobka Cieplna, Vol. 42, 1979, Pol. p. 22-7.
The present invention builds on the finding that the measurement of the adhesion of wear-protection layers on tools, such as for example the one still to be described in conjunction with examples of the invention, does not permit any reliable statements about the service life to be expected from the tools. Good layer adhesion for the tool coatings, however, is indispensable.